Officials are probing how a 51-year-old highway bridge came to collapse in the Italian port city of Genoa yesterday, killing at least 26 people and injuring 16 others as it sent dozens of vehicles tumbling into a heap of concrete and twisted steel.

High drama as parliament nears year's end

Just as much action can be expected outside parliament as inside when MPs return to Canberra for the final sitting fortnight of the year.

The High Court on Monday will hold a directions hearing into whether two senators - Family First's Bob Day and One Nation's Rod Culleton - were ineligible to be elected at the July double-dissolution poll.

The triggers for the election - bills to restore the building industry watchdog and set up a new Registered Organistions Commission - will be high on the government's legislation priority list.

The eligibility of Mr Day, who has resigned from the Senate, and Senator Culleton have the potential to change the dynamics of the upper house as their replacements could take a different approach to the government's plans.

The government has greater confidence the ROC bill will pass with the support of Senate cross benchers, but there is less certainty about the Australian Building and Construction Commission legislation.

Labor leader Bill Shorten on Friday said his party had zero tolerance for corruption in unions, politics or big business.

"It makes me sick in the guts when we see it in unions, banks or any aspect of life," he said.

With Mr Day no longer in the Senate, the government will need eight crossbench votes instead of nine.

If One Nation's four senators and Nick Xenophon's three are on board, the government will then only need to convince independent Derryn Hinch or the Liberal Democrats' David Leyonhjelm.

The cross benchers have a range of demands including greater accountability of the ABCC commissioner, support for apprentices, whistleblower protections, enforcement of Australian building standards, protections for subcontractors and changes to the 457 visa class.

The House of Representatives will kick off the week with debate on private bills to protect Christmas Day pay rates in Victoria and legislate for same-sex marriage.

Prime Minister Malcolm Turnbull won't be in parliament on Monday, as he attends the APEC summit in Peru, with his deputy Barnaby Joyce stepping into the top role.

The election of Donald Trump as US president is likely to be the focus of attention in question time, with Labor railing against American-style policy and the coalition arguing for business tax cuts and workplace reform to drive economic growth.

"I do not want Mr Turnbull to take Australia down the American path of low wages and a broken health care system," Mr Shorten said.

Superannuation will be on the agenda midweek when a Senate inquiry reports back on the government's reforms and Labor will seek to make amendments.

Uncertainty still hangs over the so-called backpacker tax after 18 months of debate and proposed changes from the government to drop the rate to 19 per cent.

Labor, the Greens and crossbenchers are seeking a 10.5 per cent rate, which could provide room for compromise.